The Stanford University Sleep Disorders and Research Center has established a multi-disciplinary research program dedicated to understanding the phenomena and elucidating the basic mechanisms of age- related disorders of sleep, wakefulness and circadian timekeeping. Reduced day-time alertness, night-time sleep fragmentation, and early morning awakenings are common complaints of older people. Age-related sleep disorders also pose significant health and safety risks as well as diminish the quality of life in this expanding portion of the population. A well focused multi-disciplinary research effort toward elucidating the basic mechanisms of circadian timing and control, and the homeostatic regulation of sleep are essential to progress on the problems of age- related sleep disorders. We have an established team of specialists and collaborators in the fields of sleep and circadian neurobiology with sufficiently diverse expertise to advance our knowledge in the area and build on significant advances made in the last few years. The proposed work is divided into 6 different but inter-related scientific projects: Project C - The aging of Circadian and Homeostatic Processes Controlling Sleep, Project D - Sleep, Circadian Timekeeping, and Aging in the Tau Mutant Hamster, Project E - The Aging Circadian Clock In Vitro, Project F - Homeostatic Determinants of Sleep Maintenance in Aging, Project G - Zeitgeber Transduction and the Aged Circadian System. The objectives of each project are based on a unifying conceptual theme -- that diminished alertness in aging can be due to age-related deterioration of the clock, impaired function of the sleep homeostatic process, or both. this research theme is founded in our Opponent Process Model of sleep/wake regulation which we believe offers a new and valuable conceptual framework for investigations into the mechanisms of sleep/wake cycle regulation in aging. The growing realization of the enormous personal and societal consequences resulting directly or indirectly from age- related sleep disorders mandate a concerted multi-disciplinary effort.